The received signal, containing a baseband signal, in a communication system generally reaches the signal receiver noisy and distorted due to a non-ideal transmission. If the signal receiver is, for example, a radio receiver and if the associated communication path is, for example, a mobile radio channel, considerble and rapidly varying distortions occur in the received signal due to multi-path propagation. During the transmission of digital data via such a channel, it is of importance for the extraction of the data from the received signal to be able to find, virtually without delay and reliably, the optimum sampling time for each of the transmitted symbols.
Known methods for clock synchronization, that is to say for adjustment to the correct sampling time at each time, are based on the detection of the zero transitions of the received signal or on a non-linear conversion (for example a squaring process) with subsequent narrow-band filtering.
The first of these methods suffers from the fact that the optimum sampling time can become displaced with respect to the time of the zero transition in the case of distorted signals.
In the second of these methods, there is also no rigid relationship between the phase of the filtered signal and the optimum sampling time. In addition, the narrow-band filtering leads to considerable delays.